Fossils
Inquiry 18.2
Purpose: What is the relationship between a fossil and the layer of rock that it’s found in?
Background information:
Read “The Position of Rock Layers” on the last page of this document. Then answer the
following questions:
1. What is the Law Of Superposition?” ______
2. What is the name of the oldest layer in the grand canyon according to the image? ____
3. What is your evidence why you think your choice is the oldest layer? __________
4. What is the age of the youngest rock layer according to the image? _____
Put your computer / tablet away so it doesn’t get dirty before continuing on with lab.
Procedures/ Experiment:
1. Place the oldest fossil from Inquiry 18.1 on the bottom of the container . (Look at your
notes to find out which of the fossils is the oldest.)
2. Put a thin layer (around 1 cm thick) of gravel in the bottom of your wide- mouthed
container and make sure it covers the oldest fossil. (In nature, the layers are called
“strata.”)
3. Now pour a thin layer of regular brown sand into your container until the gravel is
covered. Place the next oldest fossil on top of this new layer. Harden the sand into rock
by covering it with a small amount of diluted glue. (In nature, chemicals seep into
sediment and turn it into rock.)
4. Repeat Procedure Step 2 with another layer of colored sand and another fossil. Harden
the layer with diluted glue. Continue this process until all your fossils are buried (see
picture to right). Plan to bury the shark tooth in the final top layer. (What would the
top position of the shark tooth tell you about their age compared to the other fossils?
Discuss this with your group.)
5. Clean up your lab station so you only have
your container left out on the table.
6. With a marker, mark the lines of each layer
of sand and write the age of each layer
next to it. The sediment should be the
same age as its fossil. Use the age of the
fossil to determine the age of the rock. For
example, if the fossil in the bottom layer was from 440 million years ago, mark that
layer 440 MYA (Million Years Ago). If a shark tooth is on the top layer, it may have
been from 2 million years ago, so mark the top layer 2 MYA.
7. Every student needs to take a picture (with tablet) of your container from the side so that
each layer is showing with your marker lines clearly visible.
8. Bring your container to the teacher.
Inquiry 18.2 Part 2
1. Exchange your container of hardened strata with the other pair of students in your
group.
2. Can you tell how old each fossil is, based on the age of the layer in which you found it?
_____________
3. Record in the data table below the age of ALL the rock layer.
4. Excavate the fossils from the other groups container and record which fossil was found
in which layer. When excavating removing one layer at a time. Also record how old
each fossil would be if it were found in that rock layer.
Name of Fossil
Age of Fossil
Age of Rock Layer
Conclusion:
Directions: Answer the following questions in paragraph form on notebook paper:
What is the answer to the purpose / question? (See the top of the first page for help)
What is the Law of Superposition?
What evidence do you have to support your answer for the purpose? (Include all data
from the data table)
The Position of Rock Layers Reading
Have you ever seen rock layers of different colors on a cliff beside a road? What are these layers,
and how did they form? The sediment that forms sedimentary rock is deposited in flat layers one on
top of the other. Over time, the sediment hardens and changes into sedimentary rock. These rock
layers provide a record of Earth’s geologic history.
It can be difficult to determine the absolute age of a rock. So geologists use a method to find a
rock’s relative age. Geologist use the law of superposition to determine the relative ages of
sedimentary rock layers. According to the law of superposition, in horizontal sedimentary rock
layers the oldest layer is at the bottom. Each higher layer is younger than the layers below it.
The walls of the Grand Canyon in Arizona illustrate the law of superposition. You can see
some of the rock layers found in the Grand Canyon in the figure below. The deeper down you go in
the Grand Canyon, the older the rocks.